The invention relates generally to nondestructive testing (NDT) of parts and more particularly to a method and system for automatically identifying defects in NDT image data corresponding to a scanned object.
NDT is a technique of producing relevant data for an object by collecting energy emitted by or transmitted through the object, such as by penetrating radiation (gamma rays, X-rays, neutrons, charged particles, etc.) sound waves, or light (infrared, ultraviolet, visible, etc.). The manner by which energy is transmitted through or emitted by any object depends upon variations in object thickness, density, and chemical composition. The energy emergent from the object is collected by appropriate detectors to form an image or object map, which may then be realized on an image detection medium, such as a radiation sensitive detector. A radiographic detector, for example, comprises an array of elements that records the incident energy at each element position, and maps the recording onto a two-dimensional (2D) image. The 2D image is then fed to a computer workstation and interpreted by trained personnel. Non-limiting examples of NDT modalities include X-ray, CT, infrared, eddy current, ultrasound and optical.
Radiography and other NDT inspection modalities find wide application in various medical and industrial applications as a non-destructive technique for examining the internal structure of an object. Non-destructive evaluation (NDE) of industrial parts is essential for manufacturing productivity and quality control. For example, in aerospace and automotive industries, radiographic images of aluminum castings are typically inspected by an operator who identifies defects pertaining to porosities, inclusions, shrinkages, cracks, etc. in the castings. However, and as will be appreciated by those skilled in the art, owing to the structural complexity and large production volumes of these castings, the manual inspection procedure is often prone to operator fatigue and hence suffers from low inspection reliability.
A number of NDT inspection techniques such as feature-based classification, artificial neural networks and adaptive filtering have been developed to perform automatic radiographic inspections of scanned objects. These techniques are typically based on using assisted defect recognition (ADR) techniques to automatically screen images, call out defects and prioritize the ones needing visual inspection. As will be appreciated by those skilled in the art, ADR techniques typically achieve more accurate defect detection than human operators and have a much higher efficiency and consistency, thereby enhancing quality control in a wide variety of applications, such as, for example, automotive parts and engine components of aircraft, ships and power generators. Techniques using ADR may typically be used to perform automatic defect detection on 2D images and/or 3D images, based on analyzing the geometry (e.g., shape, size), feature (e.g., intensity, texture, color) and other local image statistics in the radiographic image data, to locate abnormalities. For example, ADR techniques based on image features use a set of features to identify potential flaws in scanned object parts based on flaw morphology and gray level statistics. These techniques assign each pixel in the image into one of several classes based on minimizing a distance metric, wherein the parameters characterizing the distance metric are evaluated using a supervised learning scheme. However, the performance of these techniques is affected by variations caused by object structure or flaw morphology and these techniques generally require large training sets with labeled flaws to perform defect identification.
It would therefore be desirable to develop an efficient NDT inspection technique for automatically detecting defects in the NDT image data corresponding to a scanned object. In addition, it would be desirable to develop an efficient NDT inspection technique that detects anomalies in industrial parts, produces accurate defect detection rates, increases the screening efficiency and consistency of inspection systems, efficiently utilizes system operation setup time and system training time and is robust to changes in object part geometry and misalignment of scanned object parts.